Wave stabilizer



Jan. 1, 1946.

B. DYSART WAVE STABILIZER Filed Feb. 26, 1943 PILOT sun/1.1250 m/you/Me,

T0 omen JPEPS.

J'IGNALS PILOT (2064 KC) PHASE H/F TE]? 3/ (Puma AMPLIFIER) PatentedJan. 1, 1946 WAVE STABILIZER Birney Dysart, Madison, N. J., assignor toBell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application February 26, 1943,Serial No. 477,233

4 Claims.

The invention relates to electric wave stabilizers and particularly to acircuit arrangement for effectively removing transient volume variationsrom alternating control waves.

The invention is particularly applicable to, and will be described asapplied to, automatic transmission regulating circuits such as are'usedin broad-frequency band repeatered carrier wave signaling systems tocompensate for variations in line loss due to temperature changes or tocounteract changes in the gain of the repeaters due to aging of vacuumtubes, battery variations, etc. In certain signaling systems of thistype, this is accomplished by transmitting pilot waves of frequenciesoutside the signal frequency range and of initial constant volume overthe system along with the signal waves, to control dynamic regulatorsassociated with the signal repeaters so as to provide an adjustment ofthe repeater gain determined by the amplitude of the applied pilotwaves. Such pilot waves in transmission over the system are subject tocertain transient disturbances producing ripples in the waves tending tochange the control effect on the dynamic regulators, and in a longsystem employing many such dynamically regulated repeaters in tandem,the operation of the regulators may cause the transient effect to buildup in magnitude so as to produce a considerable transient swing in thepilot waves. This may result in intolerable violent fluctuations in theintensity level of the signals at the receiving end of the system.

An object of the invention is to stabilize the volume of alternatingwaves subject to transient disturbances.

Another object isto reduce the effects of transients on signaltransmission in a long signaling system.

A more specific object is to prevent excessive transient efiects on theoperation of pilot-controlled regulators for automatically controllingrepeater gain in long repeatered signal transmission systems.

These objects are attained in accordance with the invention by the useof special circuit arrangements for deriving from an alternating controlor pilot wave transmitted over a transmis sion line, pulses proportionalto the transient volume variations r ripple components in that wave, andfor applying the derived pulses in proper phase and magnitude to thetransmission line in such manner as to effectively neutralize or balanceout the transient variations from the transmitted wave.

The various objects and feature or the invention will be betterunderstood from the following detailed description when read inconjunction with the accompanying drawing the single figure of whichshows schematically the invention embodied in a long-distance repeateredsignaling system employing pilot-controlled dynam c regulators foradjusting the gain of the repeaters.

In the drawing, the line designated I may be a transmission line in abroad frequency band multiplex carrier telephone system, for example,one employing coaxial cable and transmitting a signal frequency bandextending up to 2 megacycles. Interposed in the line I at intervals, sayfive miles apart, are signal repeaters (amplifiers) with associatedgain-adjusting regulators. two successive ones of which, designated 2and 3, are illustrated diagrammatically. The regulators of thesuccessive repeaters are arranged to be controlled in turn by a pilotwave of a given frequency, say, 2,064 kilocycles, outside the frequencyrange of the transm tted signals and of initial constant volume, whichis supplied to the line I from the source 4 near its input, and istransmitted over the line concurrently with the signal waves.

The signal repeaters 2, 3 may be of any suitable type and the associatedregulators are of the dynamic type. such as disclosed. for example, inthe patent to R. R. Blair, No. 2179.915, issued November 14, 1939, wh choperates to make the gain of the associated repeater vary directly withthe amplitude of the applied pilot wave in such manner as to restore thepilot amplitude in the output of the repeater to its normal constantlevel and thus to produce a corresponding adjustment in theamplification of t e signals, the gain regu lation follow ng veryquickly each change in pilot amplitude. Each repeater may be designed tocompensate for the loss-frequency characteristic 1 the preceding sectionof transmission line at some predetermined line temperature, and as reulated by the associated dynamic re ulator may introduce in addition avariable amount of gain, uniform over the signal frequency range ofinterest, to compensate approximately for changes in line attenuationdue to variations of temperature from the predetermined value.

In such a system the transmitted signals and pilot waves at repeater orterminal points may have transient volume irregularities init allycaused by interference of different types, such as repeater power supplyvariations and intermittent troubles, induced in the line or by changesin the operating characteristics of transmission apparatus, and which isevidenced by small ripples in the transmitted waves. The transientvolume variations or ripple components in the pilot wave may adverselyafiect the operation of the dynamic regulator at each repeater point. Ifthere is a change in the strength of the signal and pilot currents, thepilot currents will control the dynamic regulators for all of thetandem-connected repeaters and each will make a compensating gainadjustment in its associated repeater with the result thatovercompensation will be efiected. Thus, the operation of the regulatorsunder control of the pilot current will produce a transient swing of thesignal strength above and below normal value for a period of time, themagnitude of which will increase with the number of the regulatedrepeaters in tandem and may result in objectionable fiuctuations in theintensities of the signals at the receiving end of the system.

Such transient effects are reduced to an unobjectionable amount inaccordance with the invention by the use at one or more points in thesystem of a circuit arrangement such as shown schematically in thecenter of the drawing, fo stabilizing the volume of the pilot wave.

This circuit arrangement includes a hybrid coil H having series windings5 and 6 and branch windings 1 and 8 respectively inductively coupled tothe two series windings. The conductors of the incoming portion of lineI leading from the output of repeater 2, are connected directly throughthe series windings 5 and 6 of the hybrid coil H to terminals 9- and I0. The terminals of the branch winding I inductively coupled to serieswinding 5, are connected to the conductors of the outgoing portion ofline I leading to repeater 3, and the terminals of branch winding 8inductively coupled to series winding 6, are connected to an outgoingline impedance balancing network II, as shown, or to a line, which mayconstitute a spare line. The input of a control circuit I2, the elementsof which will be described in connection with the following completedescription of operation of the whole circuit arrangement, is connectedacross the outgoing portion of line- I near the hybrid coil H, and itsoutput is connected to the terminals 9, I of the hybrid coil H.

Let it be assumed that the pilot waves of given frequency (2,064kilocycles) and of initial constant volume generated bythe source 4, andsignal waves of different frequency from an input source (not shown) arebeing concurrently transmitted over the line I. 'I'hese'waves, when theyarrive at the hybrid coil H, will have small amplitude variationsforming a ripple in the wave produced during transmission over thepreceding section of line in the manner-described above. The energy ofthe received signal and pilot waves will be divided betweenthe-inductively coupled windings -I and 8, so that a portion of thesignal and pilot wave energy will pass into the outgoing portion of lineI and will pass out over that line toward repeater 3 and another equalportioninto the balancing network I I.

A portion of the wave energy in the input of the outgoing portion ofline I will pass into the input of control circuit I2 to filter I3 whichis tuned to pass waves of the pilot frequency (2,064 kilocycies) and tosuppress the signal frequencies. The pilot wave in the output of filterI3 will pass to the amplifier I4 whichis adjusted to ampl y it to thedesired degree. The output of amplifier I4 is fed in multiple to theinput of the difierential rectifier I and the input of thepulseamplifier I6.

The differential rectifier I5 includes an input transformer I5 havingtwo secondary windings I8 and IS. The input diagonal of a copper oxiderectifier bridge 20 is connected across winding I8 and the inputdiagonal of a second copper oxide rectifier bridge 2| is connectedacross winding I9. A resistance-condenser tank circuit 2: cl large timeconstant is connected across the output diagonal of rectifier bridgethrough the series variable resistor 23, and the resistance-condensertank circuit 24 of relatively small time constant is connected throughthe series fixed resistor 25 across the output diagonal of rectifierbridge 2|. The tank circuits 22 and 24 are connected together in seriesopposition through potentiometer 26, which is connected to ground asshown. The circuit constants of the two sides of the diiierentialrectifier I5 are selected so that its voltage output is zero withconstant volume pilot input applied to the input transformer H, but dueto the long-time constant tank circuit on one side, the rectifier willproduce a direct current voltage drop in the output potentiometer 26proportional to any transient variations or ripple component in theinput wave.

Other types of rectifiers may be used in place of the varistor typeillustrated. The resistor 23 is made variable to enable the output ofrectifier 20 to be balanced against that of rectifier 2| under steadystate conditions so that when no transient or ripple exists in the pilotwave the voltage applied by potentiometer 26 to bias the pulse amplifierI6 in the manner to be described, will be zero.

The pulse amplifier I6 includes the input transformer 21 having tworeversely wound secondary windings 28 and 29, two three-electrodeamplifying vacuum tubes 30 and 3| having their control grid-cathodecircuits each including a self-biasing resistor and a parallel by-passcondenser, respectively connected across'the terminals of secondarywinding 28 and of secondary winding 29 so that equal in-phase portionsof the pilot wave applied to input transformer 21 are amplified by thetwo tubes, and their plate-cathode circuits connected in push-pullthrough respective halves of the primary winding of output transformer33 and the potentiometer 34 in series between the twohalf windings,which is provided to enable an accurate adjustment of balance betweenthe outputs of the two tubes to be made.

The direct current voltage output of the differential rectifier I5 bymeans of the connection of the variable arm of potentiometer 26 to theupper terminal of transformer winding 29 in the control grid-cathodecircuit of amplifier tube 3| is used to bias the grid of that side ofthe pulse amplifier I6. The condenser 32 in the control grid circuit ofamplifier tube 3| is provided to by-pass the alternating current pilotinput to pulse amplifier I6 around potentiometer 26, and block directcurrent bias from potentiometer 26.

With constant voltage input from the output'oi amplifier I4 to pulseamplifier I6, the latter is balanced and its output remains zero. Asstated above, any ripple component or variation in the pilot volumepresent in the input of pulse amplifier I6 and differential rectifier I5causes the latter to produce a direct current voltage outputproportional to that ripple or variation in pilot volume. This voltageapplied as a bias to one side 01 pulse amplifier I 6 unbalances it sothat its pulse output, which is normally zero with constant volumeinput, is proportional to the ripple or variation in pilot volume at itsinput. The pulse output of pulse amplifier I6 is passed through, theadjustable magnitude control 35 and a phase shifter, which control themagnitude and phase of the pulses, and passes through terminals 9, linto hybrid coil H in which it is balanced against the incoming pilotwave at that point. If by proper selection and adjustment of the circuitelements in control circuit l2 the pulse output of the latter isproperly adjusted in phase and magnitude, the ripple or variations inpilot volume introduced into the input of hybrid coil H from theincoming portion of line I may be substantially balanced out. The pilotoutput of the hybrid coil H transmitted over the outgoing portion ofline I to control regulated repeater 3 is therefore free of thetransient volume variations or ripples, and its magnitude is equal tothe long-time average value of the input pilot volume.

An advantage of the wave stabilizing arrangement of the invention justdescribed is that its failure for any cause will only result in thehybrid coil pilot output having transient volume variations or ripplesequal to those at its input, and will not cause failure of thepilot-controlled regulating system.

Various modifications of the circuits illustrated and described, whichare within the spirit and scope of the invention will occur to personsskilled in the art.

What is claimed is:

1. In combination, a signal transmission line, means at one or morepoints along said line for regulating a transmission characteristicthereof, means to transmit an alternatin pilot Wave along said line tocontrol said regulating means in accordance with the volume of the pilotwave at the regulating points, said pilot wave in transmission over saidline being subjected to disturbances tending to produce small transientamplitude variations therein evidenced as a ripple in the wave, andmeans to reduce the control effect of said transient variations of thepilot wave on said regulating means, comprising means at a given pointin said line for diverting a portion of the pilot wave, transforming itinto pulses of magnitude and phase corresponding to those of thetransient variations in the pilot Wave in the line near the divertingpoint and applying the resulting pulses to the line to combine with thepilot wave therein in such manner as to neutralize to the requireddegree the transient wave variations.

2. In combination in a signaling system, a signal transmission linetransmitting signal waves and subject to variations in attenuation,signal repeaters at intervals along said line, means to send a pilotwave of a frequency outside the signal frequency and of initial constantvolume over said line along with the signals, regulating means at eachof certain repeater points, controll d by the pilot wave receivedthereat to make a continuous adjustment in repeater gain in accordancewith the pilot volume at that point so as to substantially compensatefor the efiect on the signal of the variations in attenuation of apreceding section of said line, and auxiliary means for reducing thecontrol effects on said regulating means of the ripple components of thecontrolling pilot wave caused by transient disturbances along said line,comprising means for deriving from the transmitted pilot wave at anintermediate point in said line, pulses proportional to the ripplecomponents thereof and for combining the derived pulses with the pilotwave in said line in such manner as to effectively balance out theripple components therein.

3. The system of claim 2, in which said auxiliary means comprisesfiltering means for diverting a portion of the energy of the pilot wavefrom the line at said intermediate point, an amplifier supplied with thediverted pilot wave energy, said amplifier being normally balanced so asto provide zero output for constant volume input, means controlled by aportion of said' diverted pilot wave energy for producing a directcurrent voltage proportional to any ripple components therein, means toapply said voltage as a bias to one side of said amplifier to unbalanceit so as to produce a pulsating amplifier output proportional to thevolume variations in its pilot wave input, and means to introduce theresultant pulses in proper hase and magnitude into said line near saidintermediate point in opposition to the pilot wave therein so as toeffectively balance out the ripple components from that wave.

4. The system of claim 2, in which said auxiliary means comprises meansto select from the waves transmitted over said line at an intermediatepoint therein a portion of the pilot wave and to amplify the selectedwave portion, a differential rectifier having a relatively large-timeconstant tank circuit on one side, and a pulse amplifier, supplied inmultiple with portions of the resulting amplified pilot wave, thecircuit constants of said differential rectifier being such that itprovides zero output with constant volume input and, due to saidlarge-time constant tank circuit on one side, produces a direct currentvoltage output proportional to any ripple components in the pilot input,said pulse amplifier being normally balanced so that it provides zerooutput with constant volume input, and means to apply the direct currentvolage output of said difierential rectifier, when ripple components arepresent in the input thereto, as a bias to one side of said pulseamplifier to unbalance it so as to produce a pulsating output therefromproportional to the ripple component in the pilot input, means to adjustthe magnitude and phase of the resulting pulses, and hybrid coil meansfor balancing the pulses against the pilot wave in said line near saidintermediate point so as to substantially neutralize the ripplecomponents in the latter wave.

BIRNEY DYSART.

